EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 253 AM EDT MON OCT 27 2014 VALID 12Z THU OCT 30 2014 - 12Z MON NOV 03 2014 ...OVERVIEW... A PROGRESSIVE WAVE PATTERN WITH MODERATE AMPLITUDE MIGRATES ACROSS THE NORTH AMERICAN CONTINENT THIS MEDIUM RANGE PERIOD. ...UNCERTAINTY ASSESSMENT... THE KEY FEATURES EVOLVING ACROSS THE LOWER 48 HAVE COME INTO GREATER FOCUS...WITH THE NATURE OF THE UPPER-LEVEL RIDGE OVER NORTH CENTRAL CANADA CHOOSING TO BE A PROGRESSIVE AND/OR MIGRATORY FEATURE RATHER THAN A BLOCKY/QUASI-STATIONARY ONE. THIS PROVIDES A RATHER STABLE FORECAST WITH THE PRIMARY WEATHER-MAKERS (CENTERED ON DAY 5) LOCATED IN THE NORTHERN ROCKIES AND ACROSS NEW ENGLAND. THE UNCERTAINTY IN THIS PROGRESSIVE PATTERN WILL BE THE DEPTH OF THE SURFACE CYCLONES OVER MONTANA AND MAINE...RESPECTIVELY---EMBEDDED WITHIN THESE MIGRATORY UPPER-LEVEL TROUGH FEATURES. IN THE EAST...THE CLIPPER SYSTEM MIGRATING THROUGH THE MISSOURI VALLEY ON DAY 3 AND UPPER OHIO VALLEY ON DAY 4 HAS BEEN THE 'CATALYST FOR CHANGE' IN THE PATTERN ACROSS EASTERN NORTH AMERICA. IT WILL DRAW A 1032MB+ SFC RIDGE INTO THE EASTERN THIRD OF THE NATION FOR DAY 5-7. THE SURFACE RIDGE WILL BE A DRY ONE. BUT---SECONDARY CYCLOGENESIS...SOUTHEAST OF THE 40N/70W BENCHMARK...WILL BE THE ONLY AREA WHERE LOW-LEVEL MOISTURE HAS A REASONABLE CHANCE OF GENERATING APPRECIABLE WRAP-AROUND PRECIPITATION OVER LAND AREAS---INCLUDING NEW ENGLAND. THE 26/12Z DETERMINISTIC GUIDANCE HAS SETTLED ON A CLOSED 500MB LOW SOLUTION OVER MAINE AND NEW BRUNSWICK. A MARKED DEPARTURE FROM THE 25/12Z ECMWF SOLUTION ...AND ITS 'CAROLINA' CLOSED LOW. IN EITHER CASE...THE SECONDARY CYCLOGENESIS WILL OCCUR ALONG THE LEADING EDGE OF THE COLD FRONT...PROJECTED TO BE EAST OF 70W LONGITUDE ON/AFTER 30/12Z. IN THE WEST...REMNANTS OF 'ANA' APPROACHING 140W LONGITUDE THIS HOUR...ARE NOT FAR 'OFF THE MARK'...AND THE DEEPENING UPPER-LEVEL TROUGH IN THE BERING SEA APPEARS TO BE MIGRATING EASTWARD...WHICH SHOULD BE IN THE GULF OF ALASKA---WITH A LONGWAVE TROUGH ALONG 140W LONGITUDE OF DAY 4. THIS UPPER-LEVEL TROUGH AXIS ENTERS THE WEST COAST ON DAY 5...WITH DEEPENING CYCLOGENESIS OCCURRING INLAND OVER SOUTHEASTERN OREGON/NORTHWEST NEVADA VERY CLOSE TO THE LATE FRIDAY MORNING-EARLY AFTERNOON TIME FRAME (IN DAY 4). ITS EXACT TRACK LACKING SOME DETAIL...IN PART TO THE INTENSE JET STREAK ROUNDING THE BASE OF THE UPPER TROUGH---INVOF THE SIERRA. BY DAY 5...A SUB 996MB LOW IS PROGGED TO BE INVOF 47N 110W AND BROAD WARM ADVECTION SPREADING BREEZY CONDITIONS NORTHEASTWARD THROUGH THE SOUTH CENTRAL ROCKIES AND WEST CENTRAL HIGH PLAINS. ...MODEL PREFERENCES... AS A BASELINE...THE 26/12Z GEFS/ECENS WILL PROVIDE A RATHER STABLE FORECAST FOR DAYS 3-6 AND FOR DAY 7...THE GEFS BEING A SLIGHTLY FASTER SOLUTION OVER EAST CENTRAL COLORADO. TO SMOOTH OUT THE DIFFERENCES OVER THE COLORADO ROCKIES AND WITH THE NEXT APPROACHING FRONTAL WAVE IN THE SEQUENCE ALONG THE JET AXIS IN THE FAR NORTHEAST PACIFIC ON DAY 7....A 70/30 BLEND OF THE ECENS-GEFS SHOULD KEEP THE FORECAST PROGRESSING ALONG REASONABLY WELL. THE 26/12Z DETERMINISTIC GFS/ECMWF---THROUGH THE END OF DAY 5---SHOULD CAPTURE ALL THE TRANSITORY WEATHER FEATURES MOVING FROM WEST TO EAST ACROSS THE LOWER 48...INCLUDING THE EMERGENCE OF A DEEP MID-LEVEL CUTOFF INVOF NORTHERN NEW ENGLAND AND ATLANTIC CANADA---DAY 5-6...THE SERIES OF WEAK WAVES IN NORTHWEST FLOW ACROSS ONTARIO...THE EASTERN GREAT LAKES AND NEW ENGLAND DAY 6-7. AND WITH THE DEEP SURFACE CYCLONE'S MIGRATION ALONG THE UPPER MISSOURI RIVER BASIN...FROM WEST CENTRAL MONTANA TO THE NORTH DAKOTA-NORTHWEST MINNESOTA BORDER FOR DAY 6-7. ...SENSIBLE WEATHER HIGHLIGHTS... WINDY AND WET CONDITIONS ALONG THE NORTHWEST COAST OF THE NATION---AND A MILD PACIFIC FLOW FOR DAY 3---IS QUICKLY REPLACED BY MODIFIED MARITIME POLAR AIR ORIGINATING IN THE GULF OF ALASKA FOR DAYS 4-6. THE PACIFIC COLD FRONT AND THIS COLDER AIRMASS MARCHES ACROSS THE GREAT BASIN AND THE DESERT SOUTHWEST. PLACES LIKE NEEDLES...YUMA...LAS VEGAS ...SALT LAKE CITY AND PHOENIX WILL RECEIVE A TASTE OF AUTUMN...AS HIGH TEMPERATURES FALL BACK TO SLIGHTLY BELOW CLIMO NEXT WEEKEND. IN THE SIERRA...THE MARITIME POLAR AIRMASS SHOULD BRING THE THREAT OF SNOW TO FAVORED WINDWARD SLOPES OF THE HIGH SIERRA NEXT WEEKEND. FOR THE NORTHERN ROCKIES AND ADJACENT HIGH PLAINS... WIDESPREAD DOWNSLOPE CONDITIONS ARE EXPECTED WITH NOTABLY HIGHER WIND SPEEDS... PERIODS OF HIGH CLOUDS AND RAPIDLY FLUCTUATING AMBIENT AIR TEMPERATURES DAYS 3-5. LITTLE IN THE WAY OF RAINFALL IS EXPECTED ASIDE FROM THE WESTERN SLOPES OF THE NORTHERN DIVIDE WHERE THE MID-LEVEL WARM ADVECTION IN ASSOCIATION WITH REMNANT 'ANA' MID-LEVEL MOISTURE MIGRATES EASTWARD. ON/AFTER DAY 5...THE CHANCES FOR SIGNIFICANT PRECIPITATION INCREASE WITH A WIND REVERSAL---FROM NORTHWESTERLY TO SOUTH AND SOUTHWESTERLY. IN THE EAST...THE 1032MB+ SURFACE HIGH SHOULD PROVIDE A NOTABLE DROP IN DEW POINTS FOR THE SOUTHEAST...MOST OF NORTH FLORIDA...AND PORTIONS OF THE SOUTHERN OZARKS AND SOUTHERN PLAINS---WITH DEW POINTS AROUND 40F ALONG MUCH OF THE I-20 CORRIDOR FROM LOUISIANA TO SOUTH CAROLINA. VOJTESAK